Coating compositions based on acrylic resins are used as coating agents for coating external panels of various structural elements utilized in the construction industry. However, the aforementioned coating is not sufficiently reliable with regard to water repellency, durability, and tightness of adhesion to the panels. Many attempts have been undertaken heretofore for overcoming the aforementioned disadvantages. For example, Japanese Unexamined Patent Application Publication (hereinafter referred to as Kokai) H2-64110 and Kokai H3-24148 describe curable compositions having an acryl-type copolymer with hydrolysable silyl groups as their main component; Kokai H3-252414 describes a composition that contains an acryl-type polymer with hydrolysable silyl group, an organopolysiloxane with silanol groups, and a condensation-reaction catalyst; and Kokai H7-150105 (equivalent to EP0656409) describes a composition that contains an acryl-type polymer with hydroxyl and hydrolysable silyl groups, an organopolysiloxane with silanol groups, and a condensation-reaction acceleration catalyst. However, all the aforementioned coating compositions suffer from such problems as insufficient water repellency and low endurance.
Japanese Official Patent Publication H3-69950 (equivalent to U.S. Pat. No. 4,988,788) discloses a room-temperature-curable coating composition that is formed from a siloxane-containing acrylic-type copolymer obtained by copolymerizing an alkylmethacrylate, low-molecular siloxane methacrylate, and a silane compound with hydrolysable functional groups and radical-polymerizable unsaturated groups. However, a coating film produced from the aforementioned room-temperature-curable coating composition demonstrates either low water-repellency because of an insufficient amount of siloxane units in the low-molecular siloxane methacrylate, or undesired softness and low durability because the aforementioned low-molecular siloxane methacrylate contains dialkylsiloxane units. Since the low-molecular siloxane methacrylate is produced by hydrosilation with the use of a platinum catalyst, the residual platinum catalyst left in the obtained room-temperature-curable coating composition may cause discoloration of the final coating.